lettuce portal

lettuce can be grown in many systems. the following are a few to start with –

  • By growing lettuce in an aquaponic system it can be grown year round with the addition of extra lighting indoors. To offset the cost of the lighting being able to grow lettuce year round means increased aquaponic lettuce production and higher yields. Though many different leafy greens will grow successfully in an aquaponic environment there are a variety of lettuces that do especially well. These include Bibb, Red Leaf, Oak Leaf, Pinto, Columbus, and Iceberg. Head lettuce is not usually a profitable crop because it requires a high level of nitrogen and a lot of water so by using an aquaponics system the farmer is able to provide both in abundance. The Bibb variety of lettuce is often suggested as a good beginner crop for the budding aquaponic farmer.
  • The suggested method for growing lettuce aquaponically is to create a bed for the seedlings and suspend them in a polystyrene or other foam material floating over water that has been pumped from the fish tanks. The roots need to sit in the water but not be submerged. This can also be achieved by sitting the seedlings into a thick layer of gravel and allowing the water to flow across under the roots. It is important that the lettuce not sit in water because it will cause the roots to rot and the crop to fail.

lettuce bolting

Scientists have been looking at the flowering phenomenon known as bolting to learn how we might better our odds of keeping a palatable crop.

Bolting can be seen in a variety of crops, including beets, cabbage, celery, radicchio, and lettuce, but especially in lettuce. And lettuce is the crop in which bolting has been studied most extensively. Lettuce’s penchant to bolt and turn bitter is well known. What’s less well known is why it happens.

Many say that early bolting in lettuce is accelerated by high temperatures, but experiments have shown that temperature alone is not the deciding factor. What then controls when a lettuce plant will bolt? And what causes the bitter taste connected with seed stalk formation?

here is what we know till now, we can learn and deduce what is and what is not –

Cumulative light exposure causes bolting
The discovery that lettuce’s transition from vegetative growth to bolting is influenced by cumulative periods of light was first made in Germany in 1931. Some plants in the field were simply covered so they had different daily exposures to light, and only plants given long daily periods of light bolted normally.

comment – this makes sense from the physics perspective. everything accumulates and eventually exerts its effect. light as the main source of energy should dollow the same rule.

higher temperature – bolt or not????

In 1995, William Waycott, at the United States Department of Agriculture in Salinas, California, described a number of experiments that dealt with the interaction of temperature and day length on bolting. Plants grown in plant growth chambers under short days of eight hours of sunlight at a steady high daytime temperature of 90˚F grew to harvest maturity without bolting.

Waycott also examined the bolting response in greenhouse experiments, which were started in January, when the days are short, and in July, when the days are long and temperatures sometimes reached 95°F.

Plants grown on short days bolted about 135 days after planting, compared with about 90 days for plants on long days, and neither short-day nor long-day plants had premature bolting. Thus, total day length and not temperature determined the time of bolting. This can be explained by the existence of a genetically controlled clocklike mechanism that tallies the number of light hours required for a given cultivar to bolt.

it seems that – total light exposure is the main factor in determine the bloting.

What causes bitterness in lettuce?
Scientists are sure that lettuce turns bitter after bolting. Biochemists have identified compounds responsible for the bitter taste of lettuce. These substances are in a class known as sesquiterpene lactones. These molecules have 15 carbon atoms or more arranged in rings.

The plant builds the rings in a number of steps starting with acetic acid (vinegar), which has two carbon atoms. Leaf bitterness has been highly correlated with the levels of one compound in particular, lactucin glycoside, in which the sesquiterpene is combined with a sugar molecule.

Before lettuce bolts, the bitter compounds are present at very low levels. But they increase in the leaves during flowering. Some wild lettuce species have higher concentrations of sesquiterpene lactones than domesticated lettuce. The wild lettuce has been used in breeding because it can introduce virus resistance, but breeders have had to be watchful not to introduce the bitter compounds along with the resistance.

The bitter compounds are also found in the milky juice, or latex, located mainly in the stems of lettuce. Laboratory experiments revealed that these compounds provide insect resistance. They have been shown to retard feeding by locusts, and may also act to repel burrowing insects.

here is some great comments i found by a very experienced gerderner about bolting –

A wide range of genetic expression for bolting is possible. For instance, there is a dwarf mutant of lettuce that shows extreme resistance to premature bolting and may become useful for breeding purposes. At the other end of the scale, there are mutants of crisphead-type lettuce that flower unusually early. In an experiment, a normal  lettuce flowered after 150 days in a greenhouse, whereas a mutant flowered in 55 days. In its haste to produce flowers, the mutant went from seedling to flower with­out first forming rosette leaves or heading (this is what one should be alert about in breeding). i think what we know about viagra is relevant here – let it grow fast, but block its bloting, that is the key.

here is his website you can find more details that we can learn –

http://www.vegetablegardener.com/item/5044/why-lettuce-bolts-and-what-you-can-do-about-it

 

 

 

作者: eguo

I am interested in learning new technologies, reading, and travelling.